Interpopulation recurrent selection methods can be used for developing new heterotic patterns and enhancing those identified previously. The objective of this research was to estimate the direct and indirect responses to eight cycles of reciprocal full‐sib recurrent selection in maize (Zea mays L.) populations BS10 and BS11. The populations and their crosses corresponding to Cycles 0, 2, 4,6, and 8 were evaluated at two levels of inbreeding (F = 0 and F = 0.5), and populations also were testcrossed to the respective Cycle 0 populations and unrelated inbred lines. Entries were evaluated in eight environments. Eight cycles of selection were effective for increasing grain yield of the population cross (6.5% cycle−1), BS10 (3.0% cycle−1), and BS11 (1.6% cycle−1). Standability, prolificacy, and grain moisture also were changed in the desired directions, and, in most instances, the responses were linear across cycles of selection. Direct responses were greater than indirect responses for grain yield and Standability. The selected populations also performed better than did the unselected populations in crosses with unrelated testers. Changes in inbreeding depression and heterosis were associated with selection. Rates of direct and indirect responses for grain yield in the inbred populations tended to be greater than the rates of responses in the noninbred populations. Reciprocal full‐sib selection increased the frequency of homozygotes for favorable alleles in the BS10 and BS11 populations, which would be improved sources of vigorous inbred lines with good general combining ability. Reciprocal full‐sib selection seems to have increased the frequency of heterozygotes in the population crosses.

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A better understanding of the physiological processes related to nitrogen (N) metabolism in maize (Zea mays L.) inbred lines is important for increasing the efficiency of breeding programs targeting low-N environments. This study analyzed the response to contrasting N availability of morphophysiological traits in a set of 12 maize inbred lines, from different origins (USA and Argentina) and breeding eras (from 1952 onward). Traits included in the analysis were related to canopy structure, light interception, shoot biomass production, and grain yield. Our results indicate that (i) the start of N effects on canopy size was more related to a threshold crop leaf area index (about 2) than to a given leaf stage (i.e., V n ), (ii) the light attenuation coefficient value was not affected by N availability, (iii) variations in kernel number per plant were explained by prolificacy (r 2 5 0.59), and (iv) differences in harvest index were related to kernel number per plant (r 2 5 0.77). The most important finding of our research was the detection in some inbreds of a particular response of kernel number to plant growth rate around silking, different from the general model established for hybrids. In these inbreds an additional effect of N availability was detected as reduced kernel set at a given plant growth rate under N deficient conditions (i.e., reduced reproductive efficiency). This result highlights the need of more research on reproductive sink development in this type of germplasm.

The objective of this study was to determine the relationship between the amount and type of lipids, starch composition and structure, and storage proteins on popcorn expansion and to evaluate whether popcorns could be discriminated from other types of corn based on the protein elution parameters. Seven commercial Argentinean popcorn samples were used in the study and significant differences were observed in the popping volume of these popcorns. A significant negative correlation was observed between oleic acid and popping volume and a positive correlation was observed between linoleic acid and popping volume. Popcorn starch properties were significantly different from normal corn but no particular measured attribute of starch correlated with popping volume. α‐Zein proteins and glutelins significantly correlated with popcorn expansion volume with R2 = 0.963 and 0.744, respectively. The elution patterns of corn proteins could also be used to discriminate between different types of corn including popcorn, dent, and flint corns.

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Cereal Chem. 74(1):75-78Coarse and fine kernel portions from 24 maize inbreds (six grown in two years) and four hybrids were separated by grinding and sifting. Zeins from both portions of all genotypes were analyzed by reversed-phase high-performance liquid chromatography (RP-HPLC) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Results agreed, in general, with those of a previous study in which endosperm separation was done manually, suggesting that endosperm fractionation can be done by mechanical means. Compositions of zeins, as revealed by RP-HPLC and SDS-PAGE, support the hypothesis that zeins help determine maize endosperm hardness.

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Reciprocal full‐sib recurrent selection emphasizes selection for additive and nonadditive genetic effects, and direct response is measured in the population crosses. Our objectives were to determine the contributions of additive and dominance effects to the response of selection and to estimate effects of genetic drift after eight cycles of reciprocal full‐sib recurrent selection (for grain yield) in maize (Zea mays L.) populations BS10 and BS11. The BS10 and BS11 populations and their crosses corresponding to Cycles 0, 2, 4, 6, and 8 were evaluated at two levels of inbreeding (F = 0 and F = 0.5) across eight environments for grain yield and moisture, stalk and root lodging, ear height, prolificacy, and days to anthesis. Population means were compared to estimate the contributions of genetic effects. The contributions of heterozygotes to the means of BS10CO and BS11CO were more important than homozygotes for grain yield, whereas the contributions of homozygotes were more important for grain moisture, prolificacy, standability, days to anthesis, and ear height. Significant heterosis was detected between BS10CO and BS11CO for grain yield. Heterosis for grain yield of the interpopulation crosses increased with selection and was caused by the accumulation of favorable alleles with additive and dominant effects from both populations and the heterozygous condition at loci for which genetic drift had caused fixation of alleles in one of the parental populations. Effects of genetic drift were significant for grain yield (BS10 and BS11), days to anthesis (BS10), and ear height (BS11). The improved grain yield of the parent populations over cycles of selection was attributed mainly to alleles with additive (BS11) and dominant effects (BS10). Means of selected BS10 and BS11 populations, adjusted for genetic drift, indicate that the difference between direct and indirect rates of response to selection for gram yield was not significant. The effects of assortative mating during progeny formation and small effective population sizes during recombination of selected progenies should be considered in longterm reciprocal full‐sib recurrent selection programs, particularly if improved performance of the parent populations is desired.